Electric lamp



A ril 20, 1943. e. E. lNMAN ETAL ELECTRIC LAMP Filed Jan. 10, 1941 lnvenTor': G0Tf5 E. .Inman, I A/a e C. Smifieg,

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Patented Apr. 20, 1943 2,317,061 smo'rmo LAMP George E. Inman, East Cleveland, Ohio, and Wayne 0. Smitley, Jackson, Miss., assignors to General Electric Company, a corporation of New York Application January 10, 1941, Serial No. 373,974

2 Claims.

Our inventionrelates to a method and apparatus for flashing electric discharge lamps to obtain a very intense momentary flash of light or radiant energy which may be used for photographic or signalling purposes. More particularly, the invention relates to a method for correcting for color deficiencies in the spectre of lamps of the aforesaid type. By the term flood-flash lamp, as hereinafter used, will he meant any lamp of this general type.

Hitherto in producing momentary flashes of light for photographic purposes, it has been known to subject a gaseous discharge lamp normally carrying a small holding or sustaining current to a veiy heavy current surge of very short duration. In the system described in the U. S. Patent 2,178,423 to G. E. Inman, for example, a

surge is produced by momentarily shorting a portion or all of a ballast impedance in series with th lamp. The gaseous tube in this case contains in addition t a filling of metallic vapor such as mercury a small quantity of argon gas for the sole purpose of facilitating starting. Systems of this type have not, however, attained wide usage for the reason that the color of the emitted light is not adaptable to certain ordinary photographic films such as panchromatic or color films. Such films are generally eiliciently affected only by light within certain spectral bands characteristic of the emulsion.

We have found that the aforesaid spectral deficiency can be greatly improved by adding to the lamp a quantity of gas which will emit, during the surge, light of the spectral quality desired to excite the particular film. For example, in connection with a mercury vapor tube, one may use any gas which when excited emits light of spectral quality complementary to that of the generally blue mercury spectrum such as neon gas. We have found that a lamp containing neon in this manner gives a very eiiective light for exposing Kodachrome films, for example. The added gas will not be excited to luminescence during the period when only the sustaining current is flowing since the average electron energies are too low to excite the gas which in most cases will have a high excitation potential. When the surge occurs, however, the electron energies will be much higher onthe average, and consequently, the added gas will be excited to an extent which increases with the value of the surge current. It is a further advantage of the arrangement that the added gas also acts as a starting gas to in.. itiate the metallic vapor holding discharge in the usual manner.

a lamp constructed in accordance-with the invention and an operating circuit therefor.

Referring to the drawing, the lamp comprises generally a gaseous discharge tube I enclosed within the outer envelope 2, both of which may be of a suitable transparent material such as quartz or glass. Within the envelope 3 of the tube I are provided electrodes 44 positioned on the radiating discs 5. The electrode 6 may be provided for the purpose of facilitating starting in the manner well known in the art. The electrodes 4-4 may be constructed in any of the forms common in the art, for example, they may be formed by a slug of powdered tungsten sintered to form a block and activated by a suitable material or they may be formedby a block of thorium positioned within a supporting coil of tungsten. In one example of our invention, we have spaced the electrodes 4-4 thirty centimeters apart. In addition to approximately 20 mm. of neon added in accordance with the invention, approximately mg. of mercury are introduced within the envelope. A small amount (1% by volume) of argon may also be included if it is desirable to reduce the starting voltage lower than that permitted by the neon. The mercury pressure is so adjusted that an unsaturated atmosphere obtains during the normal operation. It will be understood, of course, that a saturated atmosprhere may be used by employing an excess of mercury, but this may result in a blinking out of the lamp when heavily loaded.

The outer bulb 2 incorporates the combined support and lead members 1 which are mounted on the stem press 8. The left hand member 1 and stem press 8 also support the starting resistor 9. The coiled spring portion 10 of support 1 and the spring member II coiled about the glass tip I2 serve to position the lamp I within its outer envelope. The lead wires l3 pass through the stem to the conventional socket connections shown and serve to complete a series circuit through right hand support 1, leads M of the tube 3, the tube 3 itself, leads l5 and the left hand support 1. As

shown the starting electrode 6 is electrically connected through the resistor 9 to the left hand support I in the usual manner. A suitable inert gaseous atmosphere may be provided within the envelope 2 for'the purpose of heat insulation. For example, nitrogen at a pressure of approximately 700 millimeters may be provided.

In initiating operation, the discharge starts at the starting electrode in the usual manner whereupon a low current discharge in the starting gas develops between the main electrodes 44. The latter discharge will continue until the mercury of the tube is sufliciently heated to take over the burden of current.

In one example of our invention, we have found that the mercury discharge reached a steady state at a current of about 2 amperes with about 55 to 60 volts between the electrodes. Under this condition, approximately 3,000 lumens of light were obtained, When it is desired to flash the lamp, a surge current of magnitude dependent upon the total light desired is passed through the tube by any convenient apparatus, for example, that shown in the U. S. Patent 2,178,423 mentioned above. As an example of the range of surge currents which may be employed, the values from 60 to 200 amperes more or less may be taken. We have found that with a surge current of 130 amperes, a peak lumen output of about 450,000 lumens may be obtained.

The circuit for normal operation of the lamp I includes a conductor I5 which connects the lead l3of the lower electrode 4 to one side of the line through a switch I6, and a conductor H which connects the lead I3 of the upper electrode 4 to the other side of the line through a ballast, shown here as a choke coil I8. The starting electrode 6 is connected through the high resistance 8 to the upper electrode 4. When the switch I6 is closed, a discharge is initiated between the lower electrode 4 and the starting electrode 6 and the gas in the bulb is ionized, thereby causing the arc to start between the two main electrodes 4-4.

The lamp is caused to flash at avery high intensity by a time control means, shown within the dotted lines 20, which momentarily shunts the choke coil l8 so that, in this case, the full line voltage is applied across the lamp I. The time control means comprises a relay 2 I, the coil 22 and armature 23 of which are connected on one side through a conductor 24 and one side of a double pole switch 25 to the conductor I1, and on the other side through a conductor 26, variable resistance 21, conductor 28, and the other side of said switch 25, to the conductor I5. A resistance,

preferably in the form of an incandescent lamp 29 having a tungsten filament, which has a positive temperature coefiicient of resistance, is connected across the coil 22 of the relay 2| by conductors 30 and 3| which are connected to the conductors 24 and 26 respectively. The armature 23 of the relay 2I is normally held against the stationary contact 32 of the relay by a spring 32. Said contact 32 is connected bya conductor To operate the device, the switch I6 is first closed to cause the lamp I to operate normally, as explained above, with the choke coil in series to lower the line voltage and limit the current. To flash the.lamp and operate the camera shutter 40, the switch 25 is closed. This action shunts out the ballasting choke coil I8, the circuit then being from one side of the line through conductor l5, lower electrode 4 of lamp I, upper electrode 4, conductor 33, contact 32, armature 23, conductor 24, and conductor IT, to the other side of the line. Since the full line voltage is then applied to the lamp an abnormal current flows therethrough and the lamp emits light of extremely high intensity. The closing of the switch 25 also connects the coil 35 of the solenoid 34 across the line, thereby attracting the armature 38 and tripping the shutter control lever 39. The abnormal flow of current through the lamp I is permitted by the time control'means 20 to continue for but an extremely short time (one- I twentieth of a second, for example, with a shutter speed of one-fiftieth of a second).

The operation of the time control means 20 is as follows: When the switch 25 is closed, the coil 22 of relay 2| and the incandescent lamp 29 are also connected across th line, the circuit being from one side of the line through conductor ll, conductor 24, relay coil 22 and lamp 29 in multiple, conductor 26, resistance 21, conductor 28, and conductor I5 to the other side of the line. The time of the flash is controlled by the lamp 29, the tungsten filament of which increases in resistance as it is heated. When the switch 25 is first closed, the resistance of the cold filament of lamp 29 is comparatively low so that insufllcient current flows through the coil 22 of relay H to cause it to attract the armature 23. However. the filament in lamp 29 heats up very rapidly, thereby increasing in resistance so that sufllcient current flows through the coil 22 to cause it to attract the armature 23 and draw it away from the contact 32, thereby breaking the shunt circuit around the choke coil I8. The coil 22 holds the armature away from contact 32 until the switch 25 is opened, whereupon th spring 32' pulls the armature back against said contact 32 and the circuit is set to again flash the lamp I. The variable resistance 21 may be used to adjust the period of the flash between, for example, one-sixtieth and one-fifth seconds.

When operating normally, the lamp will show no eifect of the added neon since as is known only the spectrum of the low excitation potential mercury will predominate. When, however, the lamp is flashed, the high current density causes the neon to begin to carry part of the current and an increased amount of the red radiation character istic of that gas is obtained. The red is multiplied much more in quantity than is the green or blue of the mercury.

It will be understood that many modifications of our invention will occur to those skilled in the art to which it appertains. -For example, other gases giving spectra to which particular photographic emulsions respond may be employed in the place of the neon. The spectra of all these we intend to include within the term, complementary radiation, as used in the appended claims. Further, many variations in structural features of the lamp or in the gaseous pressures employed may be used. All these we aim to include in the scope of the appended claims.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a flood-flash lamp comprising a scaled envelope containing a pair of operating electrodes and a gaseous filling comprising a metallic vapor and a gas capable of emitting radiation in a spectral range complementary to that of said'vapor, said gas having a higher excitation potential than said vapor, means for supplying electrical energy to said lamp in sufficient amount to maintain a normal discharge therein, the pressure of :aid vapor being sufficiently high, that it carries substantially all the discharge current and the radiation emitted by the lamp is characteristic of the said vapor alone, and means for temporarily supplying to said lamp, while it is operating normally an abnormally high surge of electrical energy many times the amount normally supplied so that the electron energies are raised to a value sufiiciently high to simultaneously excite both the vapor and the gas which emit a flash of blended radiation.

2. In combination, a flood-flash lamp comprising a sealed envelope containing a pair of operating electrodes and a gaseous filling comprising mercury vapor and neon gas, means for supplying electrical energy to said lamp in sufiicient amount to maintain a normal discharge therein, the pressure of said mercury vapor being sufficiently high that it carries substantially all the discharge current and the radiation emitted by the lamp is characteristic of the mercury vapor alone, and means for temporarily supplying to said lamp, while it is operating normally an abnormally high surge of electrical energy many times the amount normally supplied so that the electron energies are raised to a value sufficiently high to simultaneously excite both the mercury vapor and the neon which emit a flash of blended radiation.

GEORGE E. INMAN. WAYNE C. SMITLEY. 

